It's kind of impossible to answer this question, really. Which is better, apples or oranges? We're not talking about a crummy game versus a good game, we're talking about two Final Fantasies. Eight came right after seven, and has therefor to live in the shadow of one of the most famous games in existence. There are a lot of similarities between Squall and Cloud, and between FF8 and 7 (mercenaries, the gunblade an attempt to not make Squall slack after Cloud's buster sword, loners that have to take the world's fate into their hands...). But, let's face it, they are both sequels in the same series - which does tend to reuse themes and ideas (to great effect, in my opinion). As with something like apples and oranges, or what kind of music you like, or what kind of milk you drink (if any). It's really just up to preference - with the exception of things like 8's better cinema graphics and 7's better mini-games. None of those traits are enough to declare either a definite superior.
That said, I would like to add that my favourite between the two is Final Fantasy 8 - most likely because I didn't own 7 until after I had already done with eight (which wasn't entirely my fault - I was advised that I could get FF7 on a Nintendo 64, and consequently didn't get a playstation until the release of FF8. I now know how silly it was to think I could get FF on a 64 - you don't have to tell me).